Data recording is a major and key portion of all data processing operations. Most data recordings employ rewritable record media, such as magnetic media. In such instances, it is common practice to store a directory of the data store in a particular record medium or record volume (such as a data storage disk, or diskette, magnetic tape, and the like). A directory to the stored data is stored in one section of the record medium, such as low-address portion; while the data is stored in the remaining portion of the record medium, such directories have been called "Volume Table of Contents (VTOC)" or "Tape Table of Contents (TTOC)".
Both the directory and data in each record medium are updated by various recording operations. Updating data includes deleting old data. Such updating associated data deletions, leave only the latest version of the data available. The historical record of data changes becomes lost, unless separate journalling or other backup operations are employed.
Some editors, such as for editing computer programs and text processors, have a limited automatic data backup facility. For example, the IBM Disk Operating System for the IBM Personal Computer employs a line editor called EDLIN as described in the Disk Operating System Manual, copyright 1981, by International Business Machines Corporation, Armonk, N.Y. This line editor creates a backup file when the user submits a "ENDEDIT" command to EDLIN. The ENDEDIT command creates a backup file identified by the suffix ".BAK" with a file name. The new file, created by the editing, has the same file name but with an extension ".XXX" specified in the EDLIN command. The directory for the new file does not link it to the backup file. The user, of course, knows the name of the file and therefore can access either the new file or the backup file. The backup file is created irrespective of the extent of editing of the file, which includes, of course, no changes whatsoever.
George, et al. in U.S. Pat. No. 4,419,725 shows a cache data store connected to a backing store consisting of a disk drive or data storage unit. Whenever the cache is written into, a new directory or segment descriptor table entry corresponding to the written to data segment is created and stored with the data written to the cache. In other words, a directory entry is stored with the data in addition to having a separate directory structure. This means that in order to read the directory entry, unless one knows the exact location of all of the directory entries, the entire cache may have to be scanned. George, et al. allocate a predetermined portion of each cache storage segment area for the directory entry. This means that the data storage areas are preferably of fixed lengths such that the location in the cache of all of the newly created descriptor table entries, are easily located. When variable length data recording is provided, this luxury of a priori information on the location of the directory entry no longer exists.
Data storage directories have included in a single entry a plurality of address pointers to a like plurality of data storage locations. For example, Hunter, et al. in U.S. Pat. No. 4,419,746 includes two addresses with each directory entry, such that two different memories can be simultaneously accessed in a single instruction cycle.
With the advent of "write-once" optical storage media having extremely high data storage density, the luxury of updating and deleting directories each time data is recorded becomes an impossibility, if the directory is to stored in the same record medium as the data itself. While one could employ a record medium having an optical portion and a magnetic portion, respectively, for storing data and directories, such an arrangement greatly increases the cost of the data recorder and, hence, is not desirable. Accordingly, for those record media having indelible characteristics (write once), it is desired to have a data storage management technique which is relatively simple for accommodating the nondelete aspects of the write once media.
Even with magnetic media, which has updatable or rewritable characteristics, the management of such data and the loss of archiving can present data processing costs; that is, various catalogues have to be constructed and stored for separately identifying where eariler versions (each version is a generation data group) of the updated sets or files of data can be found. Further, this data storage content of a volume has to be managed. Such management does require host processor and data storage control unit resources. With the cost of magnetic media being continually reduced, there is a certain attractiveness to the avoiding the resource costs of updating and deleting. Therefore, there are certain advantages in peripheral data recording of nondelete recording of data even on magnetic media, which is rewritable. Accordingly, the processes associated with nondelete recording can be applicable to wide range of data storage media.